On a remote Pacific island a mysterious lake lies hidden by dense jungle. Below the surface a gigantic shimmering phantom swims, tracking the sun. This weird life form is composed of jellyfish - millions of them - a boiling mass of medusae. Like the other bizarre inhabitants of the lake, imprisonment in this peculiar marine underworld has changed their behavior. But there are other surprises too in this first filmed exploration of the labyrinthine limestone islands of Palau - rain forests sprout from razor-sharp coral rubble; whip scorpions, giant crickets and bats haunt vast caves; and a deep lake pulsates with a strange presence.